Lingering close for connections with pipelined requests. This is expected to help with clients using pipelining with some constant depth, such as apt[1][2]. When downloading many resources, apt uses pipelining with some constant depth, a number of requests in flight. This essentially means that after receiving a response it sends an additional request to the server, and this can result in requests arriving to the server at any time. Further, additional requests are sent one-by-one, and can be easily seen as such (neither as pipelined, nor followed by pipelined requests). The only safe approach to close such connections (for example, when keepalive_requests is reached) is with lingering. To do so, now nginx monitors if pipelining was used on the connection, and if it was, closes the connection with lingering. [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=973861#10 [2] https://mailman.nginx.org/pipermail/nginx-devel/2023-January/ZA2SP5SJU55LHEBCJMFDB2AZVELRLTHI.html

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>


void
ngx_spinlock(ngx_atomic_t *lock, ngx_atomic_int_t value, ngx_uint_t spin)
{

#if (NGX_HAVE_ATOMIC_OPS)

    ngx_uint_t  i, n;

    for ( ;; ) {

        if (*lock == 0 && ngx_atomic_cmp_set(lock, 0, value)) {
            return;
        }

        if (ngx_ncpu > 1) {

            for (n = 1; n < spin; n <<= 1) {

                for (i = 0; i < n; i++) {
                    ngx_cpu_pause();
                }

                if (*lock == 0 && ngx_atomic_cmp_set(lock, 0, value)) {
                    return;
                }
            }
        }

        ngx_sched_yield();
    }

#else

#if (NGX_THREADS)

#error ngx_spinlock() or ngx_atomic_cmp_set() are not defined !

#endif

#endif

}